Self-propelled asphalt pavers having a "floating" screed ("asphalt pavers" or "pavers") are widely used for laying down asphalt pavement for highways, airplane runways, parking lots, and other construction applications. A major advantage of asphalt pavers is that they can produce a relatively smooth asphalt surface.
Asphalt pavers are usually equipped with a hopper for holding paving material which the asphalt paver is to lay down. This hopper must be reloaded with new paving material if the volume of paving material to be laid down exceeds the capacity of the hopper, as is usually the case. Three common ways of reloading the hopper have evolved.
First, a truck carrying paving material dumps the paving material on the surface over which the asphalt paver will travel. An elevating machine (which may or may not be propelled by or connected to the asphalt paver) then picks up the paving material from the surface and transfers the paving material to the hopper. The asphalt paver eventually paves over the surface on which the paving material was dumped and thus paves over any material on the surface which was not picked up and transferred to the hopper. This first approach has the disadvantage of requiring an elevating machine to pick up the paving material from the surface on which the truck dumped it and to transfer it to the hopper.
Second, a truck dumps paving material into the hopper of a transfer machine which is itself not connected to the asphalt paver. The transfer machine feeds paving material from its hopper to the hopper of the asphalt paver, typically by means of a drag flight conveyor. This second approach has the disadvantage, particularly on smaller jobs, of requiring a separate transfer machine, which also requires its own operator.
Third, a truck dumps paving material directly into the hopper of an asphalt paving machine. This third, direct-reloading approach avoids the need for the additional machine required in the first (the elevating machine) and the second (the transfer machine) approaches discussed above.
In this third approach the asphalt paver can stop moving forward while the dump truck backs up and then dumps paving material into the hopper. But completely stopping the asphalt paver while the paving material is dumped and then starting the paver moving forward again can change the balance of forces on the "floating" screed and thereby cause the screed to make a bump and/or an indentation in the pavement being laid down.
The asphalt paver will lay down much smoother pavement if it does not stop but instead remains in continuous forward motion while the dump truck reloads the hopper. Two approaches have evolved to deal with the problems of dumping the paving material directly from a truck into the hopper of an asphalt paver while the paver remains in continuous forward motion.
First, the front of the asphalt paver can be equipped with a push roller (which may be mounted on either end of a frame pivotally attached to the asphalt paver at the centerline of the asphalt paver, or which may be mounted directly on either side of the front of the asphalt paver) to contact the tires of the truck and to push the truck ahead of the asphalt paver while the asphalt paver remains in continuous forward motion and continues to lay down pavement. Although contact between the truck tire and a push roller is superior to raw contact between the asphalt paver and the truck tire, the jolt from the contact between the truck tire and a push roller can cause a jolt to the asphalt paver which may disturb the balance of forces on the screed and cause a bump and/or an indentation in the pavement being laid down. The jolt can also cause the truck to "bounce" ahead of the asphalt paver, which may also cause the truck to dump paving material on the ground ahead of the paver.
Often the asphalt paver slows down to a very slow forward speed before the push rollers contact the tires of the dump truck. But this substantial speed reduction can also change the balance of forces on the screed, causing a bump and/or an indentation in the pavement the paver is laying down.
Second, to prevent the truck from bouncing ahead of the asphalt paver, the truck wheels can be hitched to the asphalt paver with rim restraining rollers. While rim restraining rollers help keep the truck close to the paver, they do not help prevent an impact between the truck and paver that can disturb the smoothness of the asphalt surface the asphalt paver is laying down.
Thus, none of the alternatives of the prior art reliably accomplish the technical objective of permitting direct reloading of the hopper of an asphalt paver with paving material from a dump truck, while the asphalt paver remains in forward motion and continues to lay down pavement, without creating bumps and/or indentations in the pavement which the asphalt paver is laying down.